Our research program on the natural vocal communication systems of primates seeks to develop parallels between animal communication and aspects of human speech and language. The focal points of this proposal involve (1) Studies of ontogeny of vocal communication involving both structural and receptive components. We are completing longitudinal studies of vocal development from infancy through adulthood of contact calls in pygmy marmosets, and we are now able to study the offspring of these animals. We study the changes in both structure and usage of contact calls that occur with development. We will look at the development of calls in the offspring of these individuals to determine if there are vocal similarities between parent and offspring. Long calls in tamarins function much like song in birds, and we will study changes in long call structure that occur with sexual maturation in cotton-top tamarins to determine if there is a relationship between call structure and hormonal changes. (2). Studies of referential communication in pygmy marmosets and cotton-top tamarins will focus on calls given in association with food. The rate of food-associated calls will be evaluated when animals are presented with a variety of food and non-food items to determine the specificity of these calls. Individual preferences for different food types will be correlated with their preference ratings to determine if the calls simply indicate motivational state. Studies on the function of these calls will be undertaken by presenting individuals with food items not visible to other group members and determining whether calls are given and how others respond. (3) Studies of syntax or duality of patterning involving synthesis of alarm calls and contact calls of pygmy marmosets that appear to be constructed from similar elements arranged in different patterns. (4) Studies of socially interactive communication in cotton-top tamarins will be studies during the process of pair formation and after pair bonds are well established. the results of these studies should be useful in our understanding of the evolution of complex vocal communication learning to human speech and language. Our previous studies have suggested some new approaches for the study of human speech and language. Finally the results will be useful in supporting the idea that vocal communication, speech and language are processes of social interaction, where appropriate social environments and social responses are important for both acquisition and competent adult performance.